You have a formula that calls for fresh yeast. Your supermarket sells instant. Somewhere on the internet is a number that converts one to the other, and you would like it now.
We are not going to give you one, and this post is mostly an explanation of why that is the correct answer rather than an evasion.
Here is the short version. The three formats differ in water content and in viable cell count per gram. Those differences are real and they mean the substitution is not one-for-one. But the specific ratios vary by manufacturer, the widely circulated rules of thumb are approximations of unclear provenance, and the label on the packet you actually bought is the authority. Meanwhile the number that matters more than the conversion is your schedule, and almost nobody tells you that.
The three formats
Fresh yeast, also sold as compressed, cake, or baker's yeast. A moist, crumbly block. High water content, which is why it is heavy for what it does and why it perishes quickly. Refrigerated storage, short shelf life, and it is simply unavailable in a lot of places.
Active dry yeast. Dried into coarse granules. Traditionally rehydrated in warm water before use, because the drying process leaves a proportion of the cells non-viable and the dead-cell material is easier to deal with in solution. Long shelf life.
Instant yeast, also sold as instant dried, rapid-rise, or bread machine yeast, though those names are not perfectly interchangeable between manufacturers. Dried to finer particles by a gentler process, designed to be mixed straight into the flour without rehydration.
The physical difference driving everything: fresh yeast is mostly water, and the dried formats are not. So a gram of fresh and a gram of dried do not contain the same amount of yeast.
The conversion table
| From | To | Ratio |
|---|---|---|
| Fresh | Active dry | Use the active-dry maker's conversion for its product; otherwise recalibrate against the same fermentation endpoint |
| Fresh | Instant | Use the instant-yeast maker's conversion; AVPN's 2024 formula uses 1 part dry to 3 parts fresh for its specified brewer's yeasts |
| Active dry | Instant | Do not assume equal potency; use maker guidance or run matched small doughs |
| Instant | Active dry | Use maker guidance and follow the active-dry product's rehydration instructions |
The table gives a safe conversion method rather than one universal ratio. As a documented example—not a rule for every product—the AVPN 2024 regulations specify dry brewer's yeast at one third of fresh brewer's yeast in their formula.
Where a trustworthy figure comes from: a technical data sheet or usage guidance from the yeast manufacturer, stating the substitution factor for its own product, with the date you read it. Manufacturer technical literature is the right class of source here, because the manufacturer is the only party who knows the cell count and moisture content of the product in the packet. A baking-science reference giving typical figures with attribution would also do, provided it is presented as typical rather than universal.
What is not trustworthy: the ratio you remember, the ratio on a recipe site, or a ratio derived by averaging several recipe sites. Yeast quantities are small, errors in them are multiplicative over a fermentation, and a wrong number here is invisible until someone's dough fails at eleven at night. This is exactly the case where a plausible-sounding figure is worse than an absent one.
If your packet states a conversion, use that. It beats anything we could publish, because it is about your specific product.
Why the conversion is approximate anyway
Three reasons, and they apply whichever conversion you use.
Manufacturers differ. Cell count per gram, moisture content, and strain are product properties, not universal constants. Two instant yeasts from two producers are not guaranteed to be equivalent.
Viability degrades. A conversion assumes fresh product. A packet that has been open in a warm cupboard for months is not the same input as the one the ratio was derived from, and no arithmetic corrects for that.
Your schedule and temperature dominate. The effect of a modest error in yeast quantity is small compared with the effect of fermenting at a different temperature or for a different duration. Getting the conversion perfect while leaving the temperature unstated is optimising the wrong term. See fermentation is time and temperature.
The practical consequence: treat any conversion as a starting point for your first bake with a new format, then adjust based on what the dough actually did. Write down both the quantity and the result. How to log a bake sets out the fields that make the next conversion easier.
Rehydrating, or not
Active dry is conventionally dissolved in warm water before mixing. Instant is conventionally added dry to the flour. Fresh is usually crumbled into the water or the flour depending on the mixing method.
Two things to keep straight:
Water used to rehydrate is part of your formula water. Take it out of the total, do not add it. This is the same bookkeeping discipline as baker's percentages and preferment splits.
Do not dissolve yeast directly into salt. Salt in concentration is hostile to yeast, and putting undissolved yeast straight into salted water is a way to weaken it before it starts. Keep them separated until they are both dispersed in the dough.
Use the rehydration temperature and method printed by the active-dry yeast manufacturer; instant yeast may have different instructions. Count that water toward the formula and toward your desired dough temperature.
The thing that matters more than the conversion
Yeast quantity is not a fixed property of a formula. It belongs to the schedule.
A quantity appropriate for a dough mixed in the morning and baked that evening will take a dough far past where you want it over two or three refrigerated days at the same temperature. Longer schedule means less yeast. Shorter schedule means more. That relationship is more important than which format you used.
This is the single most common reason a formula "does not work" when someone changes the timeline. They scaled flour, water, and salt correctly, carried the yeast percentage across unchanged, and arrived at slack, over-fermented dough. Diagnosis and options are in over-proofed pizza dough.
We are not publishing yeast percentages by schedule length. Those depend on temperature, flour, and format, and any single figure would be false precision. Work in ranges you have established in your own kitchen, and record them, rather than treating a published figure as a point.
What you can do without any published number: change one thing at a time. If your dough consistently arrives over-fermented on a given schedule, reduce the yeast next time and keep everything else identical. Two or three bakes will land you somewhere reliable for your kitchen, and that number is worth more than a stranger's.
Storage and viability
Stale yeast is the hidden variable behind a lot of dough that "just did not rise," and it is invisible until it has cost you an evening.
- Fresh yeast is perishable and short-lived under refrigeration. Treat the stated date seriously.
- Dried formats keep far longer unopened. Once opened, they degrade faster, and warmth and humidity accelerate it. An airtight container in the fridge or freezer is the usual advice.
- Storage guidance is on the packet, and it is product-specific. We give no shelf-life figure of our own.
If you suspect a packet has gone off, test it before committing a batch: dissolve a small amount in warm water with a pinch of flour or sugar and see whether it becomes active within a few minutes. That is a qualitative check rather than a measurement, and it is enough to tell you whether to open a new packet.
Buying in bulk is economical only if you will use it before it degrades. For most home bakers, smaller packets bought more often lose less yeast than a large tin that spends a year in a cupboard.
Mistakes to avoid
Trusting a remembered ratio. Including ours, which is why there is not one.
Ignoring the label. The manufacturer knows their product. You do not, and neither do we.
Carrying a yeast percentage across a schedule change. The most consequential error in this post.
Adding rehydration water on top of formula water. It comes out of the total.
Dissolving yeast into salted water. Disperse them separately.
Assuming a substitution failure was a conversion error. Old yeast, a warm kitchen, and a changed schedule are all more likely.
In Plain English
Fresh, active dry, and instant yeast differ in water content and viable cell count, so substituting between them is not one-for-one. We are not publishing conversion ratios we cannot cite, and the packet in your hand is a better authority than any general rule, because manufacturers differ.
This is for anyone holding a formula that calls for a yeast format they cannot buy.
Use it when substituting, and treat any ratio as a first attempt rather than a fact. Take rehydration water out of your formula water, keep yeast away from undissolved salt, and check that your yeast is still alive before blaming the conversion.
Next step: whatever quantity you use, record it alongside the schedule, the temperature, and what the dough looked like at shaping. Two or three logged bakes will give you a yeast quantity calibrated to your kitchen, which is more useful than any published ratio.
Where to go next
- Read the full guide: how to choose a fermentation schedule
- The other leavening option: sourdough starter vs commercial yeast for pizza
- Why quantity follows the schedule: fermentation is time and temperature
- If you got it wrong: over-proofed pizza dough
- To scale a formula cleanly: baker's percentages for pizza
- Ingredient specs: the ingredients reference